The present invention relates to a control apparatus of an inverter for driving an AC motor, and in particular to a control apparatus capable of effectively using electromagnetic vibration tones, i.e., noises generated from an AC motor such as an induction motor or a synchronous motor driven by a PWM inverter.
As conventional countermeasures to noises generated from an AC motor driven by a PWM inverter, there are known a scheme in which the sampling frequency of the PWM inverter is raised up to the nonaudible frequency region and another scheme in which noises are changed to be white noises by changing the sampling frequency of the PWM inverter so that it may not concentrate to an identical frequency. The former scheme is described in 1986 National Convention Record, IEE of Japan, Nos. 535 and 536, pp. 625 to 626, for example. The latter scheme is described in 1988 National Convention Record, IEE of Japan, No. 523, pp. 619 to 620, for example.
Upon occurrence of overcurrent, overspeed or abnormal state in a motor, this abnormal state is generally detected and displayed on a display device or informed of by means of an alarm device.
In the former scheme among the above described conventional countermeasures to noises, attention is not paid to occurrence of high frequency noises caused by raising the sampling frequency, resulting in a problem of radio wave trouble. The latter scheme has a problem that noises offensive to the car still remain because the total pressure level of noises is not changed even if noises are made to be white.
When an abnormal state of a motor is to be informed of, it is necessary to provide a display device or an alarm device in case of the prior art, resulting in a problem of an increase of the apparatus by that amount.